A range of different apparatuses are known for the conversion of energy from water movements in bodies of water into usable energy. For example, G. Boyle, “Renewable Energy”, second edition, Oxford University Press, Oxford 2004 provides an overview of this. Apparatuses of this type are referred to within the scope of this application as “wave energy converters”.
In wave energy converters, the energy can be extracted from the water movement in different ways. For example, buoys or floats floating on the water surface are known and drive a linear generator as a result of their rising and falling movements. In another machine concept, a planar resistance element is positioned on the seabed and is tilted back and forth by the movement of the water. The kinetic energy is converted in a generator into electrical energy for example.
Wave energy converters that are arranged with their moved parts below the water surface and that utilize a wave orbital movement present there are of particular interest within the scope of the present disclosure.
The wave orbital movement can be converted by means of rotors into a rotational movement. For this purpose, rotors with coupling members, for example in the form of lift profiles and/or Flettner rotors, can be used. A system of this type is disclosed in US 2010/0150716 A1.
The rotor with its coupling members is advantageously to be largely wave-synchronous, that is to say it is to orbit with a mean speed of rotation that corresponds to the wave orbital movement or is proportional thereto. If, for example, the rotational frequency of the rotor corresponds to the wave frequency, largely static incident flow conditions are produced at the coupling members and lead to a largely continuous torque at the rotor shaft. This can be fed directly into a generator. Excessive mechanical stresses and/or nonuniformities in the output power of the wave energy converter can thus be avoided.
In particular in the open sea, rather different wave states occur however. Bedsides what are known as deep seas, in which the waves occur very regularly, these wave states also include wave states in which the wave characteristic changes continuously as a result of the superimposition of different waves. Within the scope of this application, the first wave state is referred to as a “monochromatic” wave state, and the second wave state is referred to as a “multichromatic” wave state. Completely monochromatic wave states occur rarely in nature, and therefore the term “monochromatic” also includes waves that have a certain, albeit low, multichromatic component.
Although the wave states generally do not change suddenly and in addition can be relatively well predicted, the speed of rotation of a corresponding rotor often cannot be adapted quickly enough in practice. This is true in particular for multichromatic wave states.
The disclosure therefore attempts to create a possibility of improving the synchronizability of a wave energy converter, even in the case of multichromatic wave states.